52 THE PRINCIPLES OF MYODVNAMICS. 



joint becomes relatively less as the dynamic 

 angle becomes less than a right-angle, in the 

 case of any bony lever. The displacing compon- 

 ent is a factor of instability. 



37. By the formulae of the component tri- 

 angle, 27, (b); when two sides of the dynamic 

 triangle and one of the related forces are known, 

 it is possible to find either of the other two 

 forces. — The dynamic triangle is the component 

 triangle of the lueight. 



38. There are two important facts in regard to 

 the structure of joints that ought to be remem- 

 bered : — In myodynamics (a) the ligaments al- 

 ways and (b) the conformation of the joint 

 sometimes antagonize the displacing components 

 of the power and the weight. The crucial liga- 

 ments of the knee-joint and the conformation of 

 the hip-joint are especially adapted to antagonize 

 displacing components. — In the wrist joint the 

 displacing components are small and the reten- 

 tive components are large. 



39. When the displacing components are suc- 

 cessfully antagonized by the articular ligaments 

 and the articular conformation, the forces of 



